A two-coil solenoid device comprising a cylindrical metallic armature mounted within a housing for axial movement between a first electromagnet and a second electromagnet, each located at a respective end of the housing adjacent to a respective end of the armature, is known from GB 2189940A.
Movement of the armature from closely adjacent to the first electromagnet to closely adjacent to the second electromagnet is achieved by switching on both electromagnets and subsequently switching off the first electromagnet. Subsequent to this, the second electromagnet may be switched off. The armature can be made to move in an opposite direction by again switching on both the electromagnets and subsequently switching off the second electromagnet.
One disadvantage of this method of controlling armature movement is the existence of dead-time between switching on the electromagnets and their reaching steady state current flow through their coils.
Another disadvantage is the increased consumption of power and resultant heat build-up in the device due to the electromagnets being switched on for overlapping periods.
It is an object of the present invention to provide an improved method of operating a two-coil solenoid valve (TCV).
According to a first aspect of the present invention, there is provided a method of operating a two-coil solenoid valve of the type comprising an armature member located in a housing for movement between a first electromagnet and a second electromagnet, each electromagnet being located adjacent to a respective end of said armature member and being switchable between an on state and an off state, wherein, to move the armature member from a first position closely adjacent to the first electromagnet to a second position closely adjacent to the second electromagnet, the electromagnets are controlled to be at the same initial switched state and subsequently one of said electromagnets is switched to said other switched state for a first predetermined period sufficient to allow the resultant pull exerted on the armature member to be such that the armature member is caused to move towards the second electromagnet, the duration of the first predetermined period being such that said one electromagnet is switched back to its initial switched state before the armature member reaches said second position.
The method may be such that the electromagnets are controlled to be initially at their switched on states prior to being controlled to cause movement of the armature member.
The method may also be such that, after the armature member has reached the second position, the second electromagnet is controlled to be switched to its off state for a second predetermined period, the duration of this period being such that a steady state current flowing in a coil of the second electromagnet decreases to a lower steady state current level which is sufficient to maintain the armature member in said second position prior to a subsequent further switching off of the second electromagnet for a further predetermined period to cause movement of the armature member to the first position.
Alternatively, the method may be such that the electromagnets are controlled to be initially at their switched off states prior to being controlled to cause movement of the armature member.
The method may be used to operate a two-coil solenoid valve in which the armature member is a longitudinally extending valve member and in which the armature member may be arranged to move axially between the electromagnets.
According to a second aspect of the present invention, there is provided a two-coil solenoid valve for implementing the method according to the next five preceding paragraphs, wherein at least one electrically controllable switching means is provided for switching the electromagnets on and off.